mount: dump one file system only once (v2)

A file system can be bind-mounted a few times and some of these mounts
can be non-root. We need to find one of root mounts and dump it.

v2: don't forget to check pm->dumped and pm->parent
    don't dump a root file system, it's always external for now.
Reported-by: Saied Kazemi <saied@google.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/proc_parse.h

@@ -117,7 +117,10 @@ struct mount_info {
 	struct fstype	*fstype;
 	char		*source;
 	char		*options;
-	bool		mounted;
+	union {
+		bool		mounted;
+		bool		dumped;
+	};
 	bool		need_plugin;
 	int		is_file;
 	bool		is_ns_root;

mount.c

@@ -932,8 +932,17 @@ static int dump_one_mountpoint(struct mount_info *pm, int fd)
 			pm->root, pm->mountpoint);
 
 	me.fstype		= pm->fstype->code;
-	if (!pm->need_plugin && pm->fstype->dump && pm->fstype->dump(pm))
-		return -1;
+
+	if (pm->parent && !pm->dumped && !pm->need_plugin &&
+	    pm->fstype->dump && fsroot_mounted(pm)) {
+		struct mount_info *t;
+
+		if (pm->fstype->dump(pm))
+			return -1;
+
+		list_for_each_entry(t, &pm->mnt_bind, mnt_bind)
+			t->dumped = true;
+	}
 
 	me.mnt_id		= pm->mnt_id;
 	me.root_dev		= pm->s_dev;